Immersion development



Nov. 20, 1962 w. B. THOMPSON 3,064,622

IMMERSION DEVELOPMENT Filed June 20, 1960 INVENTOR. ILL IAM B. THOMPSONATTORNEY VOL 71465 SOUR CE United States Patent @fitiee 3,064,622Patented Nov. 20, 1962 3,064,622 IMMERSION DEVELOPMENT William B.Thompson, Columbus, Ohio, assignor, by mesne assignments, to XeroxCorporation, a corporation of New York Filed June 20, 1960, Ser. No.37,380 3 Claims. (Cl. 118-637) This application deals withelectrostatics and more particularly with image development in the artof Xerography.

In the art of xerography it is customary to form a latent electrostaticcharge pattern on the surface of a Xerographic plate including aninsulating, generally photoconductive insulating layer. The latentcharge pattern is then generally utilized by being made visible throughthe electrostatically controlled deposition of finely divided markingparticles. Various different Xerographic development techniques areknown in the art. The present invention is concerned with an improvementof liquid immersion development.

According to this invention the Xerographic plate is developed by beingimmersed in a dielectric liquid medium. Fine particles in a liquidcharacteristically acquire an electrostatic charge depending on theircomposition, and are selectively attracted to charged or unchargedportions of the Xerographic plate. It is obvious that a xerographicplate can be developed equally well by contacting the surface to bedeveloped with a film of liquid or by pouring a stream of liquiddeveloper across the surface, and such modifications are intended to beincluded in the term immersion as used in this specification and claims.

Liquid immersion development, in common with most other forms ofXerographic development, is better adapted for the development of linecopy images than for the development of continuous tone images. Wherelarge areas of charge are found on a Xerographic plate, or where thegradations of charge from one point to another are slight, as withcontinuous tone images, the electro static lines of force bend back intothe plate rather than extend outwardly adjacent to the plate. Since itis the attraction of developer particles by external lines of force thatcauses development, the absence of such lines leads to no development orinadequate development. Accordingly, most Xerographic developmenttechniques fail in some degree to deposit developer particles in afaithful relation to the electrostatic charge pattern on the Xerographicplate. In accordance with the present invention, however, these problemsare eliminated, and improved image quality is obtained through the useof a magnetic member in a liquid immersion system.

It is accordingly an object of the present invention to improve liquidimmersion development.

It is a further object to provide methods and apparatus for improvingcontinuous tone reproduction and solid area coverage in liquid immersiondevelopment.

It is a still further object to provide a liquid immersion developmentmethod employing a magnetic member.

These and further objects will become apparent from the followingspecification and drawings, in which:

FIG. 1 shows the formation of a magnetic brush;

FIG. 2 shows Xerographic development being carried out according to theinvention;

FIG. 3 shows an embodiment of a suitable form of magnet; and,

FIG. 4 shows an embodiment of automatic development apparatus accordingto this invention.

FIG. 1 shows a magnet 10 being inserted in a container 11 partiallyfilled with magnetic particles 12. Particles 12 are attracted by magnet10 and form a brush-like structure 13 about the end thereof. Thisstructure persists as magnet 10 is removed from container 11 and thecomposite is generally referred to as magnetic brush 9.

Magnetic particles 12 should be magnetically attractable and at leastsufiiciently conductive so that they are incapable of retaining anelectrostatic charge for any appreciable time. Virtually all magneticparticles are sufficiently conductive to meet this requirement, andaccordingly, various powdered magnetic metals and metal alloys, as wellas metal oxides, ferrites and the like may be employed. In addition, theparticle size employed should be small, but at least an order ofmagnitude larger than that of the developer particles which, as will bediscussed later, are preferably a few microns in diameter or less. Aparticularly suitable, inexpensive, and readily available material formagnetic particles 12 is about 200 mesh iron filings.

FIG. 2 shows how the magnetic brush of FIG. 1 is employed in adevelopment process. As shown, a xerographic plate 14 comprising aninsulating layer 15 overlying a support layer 16 is immersed in a liquiddeveloper 17 which is contained in tray 18. The nature of plate 14 andliquid developer 17 will be discussed at a later point. As shown,magnetic brush 9 is also immersed in liquid developer 17 and the endbearing brush-like structure 13 is brushed over the surface of plate 14.Since brushlike structure 13 is soft and flexible, it may be drawnmagnetic brush 9 does not discharge the electrostatic.

charge pattern on plate 14, even though the particles comprising brush13 are themselves conductive. Presumably, the liquid forms a thininsulating film separating brush 13 from plate 14. The liquid may alsoinfil-.

trate brush 13, thus insulating the individual particles from eachother. If this occurs, the capacitance between the individual particlescomprising the brush is still sufficiently high so that the brush isstill effectively an equipotential body.

Xerographic plate 14 used in this invention may comprise any of theforms known in the art. Thus, insulating layer 14 may comprise anyinsulating material, such as polystyrene, capable of retaining a chargepattern for a reasonable period of time, or it may comprise aphotoconductive insulating material such as vitreous selenium, adispersion of zinc oxide in an insulating binder, or various othermaterials known in xerography. Support layer 16 may comprise anysuitable mechanical support, whether rigid or flexible, such as metal,paper or the like. Layer 16 may also be dispensed with where layer 15itself has adequate strength.

Liquid developer 17 comprises a suspension of finely divided particlesin a dielectric liquid. The liquid itself must be sufficientlyinsulating to prevent dissipation of the electrostatic charge pattern onplate 14. This generally requires a volume resistivity in the order 10to 10 ohm-centimeters or greater. Suitable liquids include among othersnormal heptane, normal hexane, petroleum ether and various commercialpetroleum solvents having volatility in the kerosene to gasoline range.Suitable liquids of this latter type include Sohio OdOrless Solvent#3440, available from the Standard Oil Company of Ohio; commercialkerosene; Shell 140 solvent and Shell 8230 insecticide base, bothavailable from the Shell Chemical Corporation; and, Soltrol 130,available from the Phillips Petroleum Company. Where non-flammableliquids are desired, use can be made of carbon tetrachloride,tetrachloro-ethylene, trichloro-ethylene, and tri- Various other liquidshaving the necessary resistivity can also be used as the liquidcomponent of liquid developer 17.

The particles used in liquid developer 17 may also comprise varioustypes. They may, for example, comprise finely divided pigmented resinparticles of the vinyl, acrylic or other types, finely divided drypigments, fine particles of dyes insoluble in the dielectric liquidemployed, or artists oil pigments disperse in the liquid. Other usefulforms of particles include carbonyl iron powders, available from theAntara Products Division of General Aniline and Film Corporation, aswell as finely divided iron oxide particles. These latter two types ofmaaterials have, of course, magnetic properties, but are neverthelessquite useful in carrying out the present invention. Apparently, whensmall particle sizes are employed, the electrostatic forces tending toattract the particles to the electrostatic latent image on plate 14 aregreater than the magneic forces exerted by magnet which might tend toremove the particles from plate 14. All types of particles, whethermagnetic or otherwise, are preferably employed in a size range of a fewmicrons or less in order to avoid an objectionably grainy appearance inthe developed image. The optimum concentration of the various types ofparticles is variable, but generally lies in the range of .1 to 1% byweight. A requisite for the developer material is that itbe insoluble inthe dielectric liquid.

FIG. 3 shows one of various other forms of magnets which may be used incarrying out the present invention. Magnet 19, as shown, is of generallycylindrical form but with an even number of alternating longitudinalflutes and ribs. As shown, each rib constitutes a magnetic pole ofpolarity opposite to that of the next adjacent rib. When such a magnetis dipped in iron filings or the like, a u

magnetic brush is formed which extends the full length of the magnet andis nearly continuous around the circumference of the magnet. This formof brush makes magnet 19 particularly suitable for use in an automatictype of liquid immersion developing apparatus.

' FIG. 4 is a schematic illustration of one form of automatic apparatusembodying the present invention. As shown, there is included adeveloping tank or tray 18 filled with a liquid developer 17. Ahorizontal cylinder 20 is partially immersed in liquid developer 17 andis adapted to be rotated about its axis by conventional means not shown.A flexible web-like xerographic plate 21 is led around the lower portionof the circumference of cylinder 20 and is thus passed through liquiddeveloper 17'. Magnet 19, of the same type as shown in FIG. 3, ispositioned beneath while substantially co-axial with cylinder 20. Magnet19 is mounted on a shaft 25 and with its adherent magnetic brush-likestructure 13, is adapted to be rotated about its axis by further drivemeans, provided by motor M-1 operatively connected via belt and pulleycombination 26 to shaft 25, so that brush-like structure 13 contacts thelatent image bearing surface of xerographic plate 21. Thus, as theapparatus is in operation, xerographic plate 21 is continuously ledthrough a path of liquid developer 17 and all portions of plate 21 arecontacted by the brush-like structure 13 adhering to rotating magnet 19.There is thus provided simple apparatus for effecting high qualitycontinuous tone development of a xerographic plate in the'form of amoving flexible web. As a further modification of the apparatus of FIG.4, plate 21 could be eliminated and cylinder 20 could be replaced by acylindrical xerographic plate together with suitable conventionalapparatus for forming an electrostatic latent image thereon.

Since this invention deals with the art of xerography, variousconventional Xerographic methods and apparatus for forming electrostaticlatent images, transferring and fusing developed images, etc. may becombined with the invention. Similarly, various forms of magnets, notshown herein, will readily occur to those skilled in the art. These andvarious other modifications are intended to be encompassed within thescope of the appended claims.

What is claimedis:

l. Xerograpln'c developing apparatus comprisinga container adapted tohold a Xerographic liquid developer, magnet field means positioned anddisposed within said container and within'the area of'said containercovered by the liquid developer when said container bears liquiddeveloper, said magnet being substantially cylindricalin shape andhaving formed on its periphery longitudinal flutes and ribs, each ofsaid ribs constituting a magnetic pole of polarity opposite to that ofthe next adjacent rib as to be adapted to maintain a brush-likestructure of magnetic material on its outer surface, means to positionan electrostatic image bearing surface within said container and intovirtual contact with a brush-like structure on said magnet, and means toeffect driven relative movement between the magnet and said imagebearing surface whil in said last-recited relation whereby to depositmarking material from liquid developer in said container on theelectrostatic image on the image bearing surface.

2. Apparatus according to claim 1 including" roller means to move theimage bearing surface relative to said magnetic brush within saidcontainer.

3. Apparatus according to claim 2 including motor connected drive meansto rotate said cylindrical magnet during development of theelectrostatic image on the image bearing surface concomitantly with themovement of said image bearing surface.

References Cited in the file of this patent V UNITED STATES PATENTS2,786,439 Young Mar. 26, 1957' 2,854,947 Giaimo Oct. 7, 1958 2,898,279Metcalfe et al. Aug. 4, 1959 2,907,674 Metcalfe et a1 Oct. 6, 1959-3',043,684 Mayer July 10, 196

FOREIGN PATENTS r 755,846 Great Britain Aug. 22, 1956

